[Bug c++/47964] New: logical || returns false result, optimization level 02 or 03

[Bug c++/47964] New: logical || returns false result, optimization level 02 or 03

[rob.bob.301 at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

           Summary: logical || returns false result, optimization level 02
                    or 03
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rob.bob.301@hotmail.com


A very simple expression 
return a < C || ~a < C;
 produces incorrect result if compiled with optimization level O2 or O3.
"a" is an unsigned, "C" is const unsigned,
gcc (SUSE Linux) 4.5.0 20100604 [gcc-4_5-branch revision 160292].
Optimization levels O1 and O0 work fine.

Note that all works fine if compiled with O2 or O3 and gcc version
gcc (SUSE Linux) 4.3.2 [gcc-4_3-branch revision 141291]

Valgrind reports no errors. Please read the few lines of code below.
Please read cout statements, and the printout. They demonstrate the
problem. t_mdb_id is unsigned (typedef).
You will see that the same logical || in cout also produces incorrect
results.
The function is in anonymous namespace.
When I copy the function to a simple
project the problem disappears. 
Note that removing "inline" changes the result to the correct 
value if cout statements stay as they are, but does not change the 
result if complied with cout statements commented out.


inline bool is_valid( t_mdb_id a0 )
{
std::cout << " a0: " << a0 << " ~a0: " << (~a0) << " cv: " <<
exampler::CONST_VOID << std::endl;
std::cout << " l: " << (a0 < exampler::CONST_VOID) << std::endl;
std::cout << " r: " << (~a0 < exampler::CONST_VOID) << std::endl;
std::cout << " is: " << ((a0 < exampler::CONST_VOID) || (~a0 <
exampler::CONST_VOID)) << std::endl;
  return a0 < exampler::CONST_VOID || ~a0 < exampler::CONST_VOID;
}


-----------------------
 a0: 1 ~a0: 4294967294 cv: 1000001
 l: 1
 r: 0
 is: 0
-----------------------

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-03 09:11:43 UTC ---
You need to provide self-contained testcase, this is not self-contained.

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2011.03.03 10:13:18
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-03 10:13:18 UTC ---
Self-contained as in, compilable and runnable and showing the failure.

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-03 10:17:45 UTC ---
bool foo (unsigned int a0)
{
  return a0 < 1000001U || ~a0 < 1000001U;
}

int
main ()
{
  __builtin_printf ("%d\n", (int) foo (1));
}

certainly prints one, not 0.

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[rob.bob.301 at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

--- Comment #4 from rob.bob.301 at hotmail dot com 2011-03-03 18:26:00 UTC ---
(In reply to comment #1)
> You need to provide self-contained testcase, this is not self-contained.

Thank you for running your simple experiment. Unfortunately, all my attempts to
create a simple self-contained test have failed. Of course, during this
process, I did play with exactly the same code you did. 
I have been aware of this problem for several months. I decided to file a bug
without a test because the problem appears to be critical and I hope somebody
who knows the optimization code might spot the issue.
All I can add is that my project is about 110k lines of code, the function in
question is in a .cpp file of about 560 lines. But I doubt it helps very much.

S.

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-03-03 19:03:47 UTC ---
(In reply to comment #4)
> Unfortunately, all my attempts to
> create a simple self-contained test have failed. Of course, during this

The advice here may help you:

http://gcc.gnu.org/bugs/minimize.html

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[rob.bob.301 at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

--- Comment #6 from rob.bob.301 at hotmail dot com 2011-03-05 21:28:26 UTC ---
This bug is not present in 
gcc (SUSE Linux) 4.4.1 [gcc-4_4-branch revision 150839]

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-29 16:51:47 UTC ---
Is this still present on the 4.5 branch, or later releases?

(In reply to comment #4)
> (In reply to comment #1)
> > You need to provide self-contained testcase, this is not self-contained.
> 
> Thank you for running your simple experiment. Unfortunately, all my attempts to
> create a simple self-contained test have failed.

It doesn't necessarily have to be simple (although that's preferable) but
without a testcase of some kind this will not get looked at.

[Bug c++/47964] logical || returns false result, optimization level 02 or 03

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47964

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|                            |INVALID

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-23 21:31:24 UTC ---
Feedback not forthcoming.